Variable pulley transmission assemblies known in the prior art comprise variable sheave pulleys, a connecting belt and a control unit. In automotive applications it has generally been necessary to utilize hydrodynamic and/or clutch assemblies as starting devices, and some arrangement to effect a change of direction. One suitable arrangement is a forward-reverse gear mechanism having planetary gearing and separate clutches. Planetary gearing also provides a desirable gear reduction. Alternatively, a change of direction can be accomplished with a reversal of the pulley rotation. This method of directional change, assuming low belt ratio, requires stopping pulley rotation and initiating motion of the drive train members in an opposite direction. Further, a change of belt ratio when the pulleys are stopped requires that the belt be slid across the pulley faces causing wear on both the belt and the pulley surfaces, and requires a great deal of force to perform such a belt movement.
A significant improvement in variable pulley transmissions is described in the application of Richard L. Smirl entitled "Variable Pulley Transmission", Ser. No. 257,283, filed Apr. 24, 1981, and assigned to the assignee of this application. As there taught a variable pulley transmission assembly is coupled between a prime mover and a driven means. The assembly includes, in order, from the prime mover, a vibration damper, input and output movable sheave pulleys connected by a flexible belt, a belt ratio control arrangement, a wet clutch, a forward-neutral-reverse gear arrangement and connecting elements to a drive means, generally a differential drive system with ring and pinion gear set. This apparatus is adaptable for use with an automobile where the engine is the prime mover and the final drive means is a differential-axle-wheel assembly.
In that application, a primary variable sheave pulley is mounted on an input drive shaft to which a vibration damper is drivingly connected, and which damper is affixed to a flywheel. A secondary variable sheave pulley is mounted on a second shaft, and connected to the primary pulley by a flexible belt such that the pulleys are continuously rotating during engine operation. In that application the secondary pulley is connected through a sleeve to a slippable, fluid actuated starting clutch, generally referred to as a wet or oil-cooled clutch. The starting device is responsive to prime mover speed. Also included in this starting device is a forward-neutral-reverse selector mechanism. Such an arrangement provides a continuously variable pulley transmission mechanism (CVT) where the pulleys are in continuous rotation during prime mover operation, which rotation provides ease of belt ratio shift even at a stopped or idle position of the driven means. However, control arrangements in the prior art are not suitable for optimum regulation of such a CVT, and it is thus a primary consideration of this invention to provide such an improved control arrangement.